1. Technical Field
The invention relates to a roll for thermal and mechanical treatment of a web-shaped product, the roll comprising an elongatable thermal rim insulation.
It is regularly striven to construct heated or cooled rolls for thermal and mechanical treatment of web-shaped products so that the surface temperature is uniform over the full contact area. The shape of the roll is also required to remain as created at ambient temperature despite thermal expansion, this being the only way to also ensure that the pressure in the nip is uniform.
One particular problem in this respect is always the rim portion of the roll or, more precisely, the portion in which the web-shaped medium ends. It is here, for example, in heated rolls that the elevated reduction in heat by the web ends, and heat is given off to the environment only by convection andxe2x80x94usually negligiblexe2x80x94radiation. Since this heat flow is significantly less than that in the web, the temperature increases in the surface portion of the roll having no web contact. Due to heat conduction beneath the surface of the roll, this increase in temperature usually extends also into the edge portion of the web, where it has a negative effect on the results of treatment.
This increase in temperature also involves thermal expansion of the roll diameter, resulting in a reduction in the nip in the edge portion of the paper web, where the specific pressure on the web increases and leads to a further negative effect on the results of treatment. If, in a paper calender, the web is overpressed at the ends in this way, the paper becomes thinner and loses its stiffness.
When the hot rim portion of a roll comes into contact with the companion roll, this may also result in damage if, for instance, the companion roll is coated with a temperature-sensitive flexible coating.
2. Description of Related Art
The measures proposed and also taken in attempting to solve the problems associated with rim heating are numerous. Correspondingly extensive is the prior art literature in this respect. For example, cited here is DE 31 40 425 regarding a roll having a shrink-fit positive displacer. It is intended that the heat flow be reduced from the heat transfer medium to the surface of the roll by an internal insulation. This reduces both the surface temperature and the expansion or so-called oxbow effect associated therewith in the rim portion.
In the case of rolls heated via a heat transfer medium flowing in axial-parallel conduits near to the surface of the rolls, rim insulation with higher heating performance has become prior art. In this case, the insulation is achieved by tubes or shells of an insulating material, such as, for example, Teflon, inserted in the edge portion of the conduits.
Since the expansion of the roll trunnion also affects the shape of the roll body in the rim portion, the insulation was also extended to the trunnion area of thermal treatment rolls, DE 35 18 808 C2 being an example of this. This requires, in general, that ovalization of the usually tubular roll body under linear pressure, the stiffening effect of the trunnion and the differing expansion coefficients of the materials, be carefully adapted to the measures taken in insulation.
Common to all of these means of optimization is that they can only be defined for a specific operating condition, i.e. as soon as the operating conditions such as, for example, the web width or the temperatures change, then the disadvantages cited at the outset reoccur more or less severely. Apart from this, taking into account all of the influencing factors involved is very difficult. Even after optimization there is often the need to adapt the dimensioning of the insulating measures as selected in design to the operating results as actually observed.
This is why there has been no lack of proposals to configure heating in the rim portion variable in order to also keep as much as possible to the optimum distribution of temperature and pressure given changes in the operating behavior.
Representative of this, a few proposals are cited from prior art in this respect.
Thus, it is proposed, for example, in DE 30 14 891 A1 to provide separate thermal treatment of the rim portions of heated rolls by means of separate heat transfer medium circuits. This idea presupposes the availability of rotary ducts having more than two connections when only one trunnion is available for the input and output of the heat transfer medium. As far as is known, no rotary ducts exist with the necessary cross-sections and the idea has never been put into actual practice.
In DE 43 43 172 C1, it is proposed for peripherally drilled thermal treatment rolls to provide several inputs for the heat transfer medium in the roll body, which intercept the peripheral drillings at various distances away from the rim. Using externally operable gate valves, the heat transfer medium can then be input and output at various distances away from the rim. However, such a variable rim heating was likewise never achieved, because weakening the highly loaded roll body in the rim portion by a plurality of communicating drillings is not without its problems.
In DE 31 40 425 A1, it is proposed, for a positive displacer roll, to employ an axially shiftable thermal insulating sleeve over a positioner guided outwards by means of a screw thread for thermally influencing the rim portion.
The same idea is to be found in DE 42 44 812 C2, however, for a peripherally drilled roll shell and, thus, applied to the insulating tubes used therein. As in DE 31 40 425, the intention is to provide external axial shifting of a sleeve of insulating material by rotating a positioner, guided externally, on which a screw thread is fitted.
However, to date, axially shiftable insulating sleevesxe2x80x94either in positive displacement rolls or in peripherally drilled rollsxe2x80x94have not entered practice.
The reason for this would seem to be the decisive sealing problem involved. Thus great care is taken to seal off the oil-guided portions from loss of the thermal oil in the case of modern thermal oil-heated rolls, in which the thermal oil is directed via distribution conduits in the trunnion flanges to the peripheral drillings. Such rolls are designed, more particularly, with double-acting sealing systems in which the oil needs to overcome two seals in sequence, before any leakage can occur. DE 42 44 812 C2 requires, for each side of each peripheral drilling, an additional sealed rotary duct to the exterior for the positioners.
Positioning the insulating sleeves in common at one side of the roll is not possible. Each sleeve needs to be moved individually. This is also the case in positioning the insulating ring on the positive displacer roll according to DE 31 40 425 A1, since a single adjusting screw would distort the ring.
Finally, there is no outward indication of the momentary positions of the individual axially shiftable insulating sleeves. It is thus easy to imagine that even minor negligence of the operating personnel and incomplete documentation of the positioning procedures may result in total disorientation as to the position of the sleeves, which can then only be established after having dismantled the roll trunnion.
Simply shifting the insulating sleeves is disadvantageous since a shift towards the middle of the roll exposes a non-insulated portion at the roll rim, resulting in the roll body being heated at a location where no heat is taken away.
Adjusting the thermal effect of the trunnion portion at the drive end of thermal treatment rolls is the subject matter of DE 195 13 500.8-12, Part of the heat transfer medium flow is directed through the central portion of the trunnion to enhance adapting the trunnion diameter to the changing operating temperatures via the heating in this portion, i.e. the shape of the roll in the rim portion is changed via the shape of the trunnion and not by the temperature of the roll body itself.
An object of the invention for a roll for thermal and mechanical treatment of a web-shaped product, comprising peripheral thermal treatment conduits for a thermal treatment fluid, is to achieve an elongatable rim insulation of the thermal treatment conduits which is reliably sealable and simple in design.
A roll, as defined by the invention, comprises a roll body having thermal treatment conduits for a thermal treatment fluid, which port at or in the vicinity of at least one face end of the roll body. The thermal treatment fluid may serve to heat or cool the roll shell and the web-shaped product. The thermal treatment conduits are oriented preferably in the axial direction of the roll body and are, more particular, preferably configured as axial peripheral drillings. Configured in a thermal treatment conduit at the end of the roll body by an insulating device is a thermal rim insulation between the thermal fluid flowing through the thermal treatment conduits and the roll body. The roll comprises furthermore a trunnion flange secured, preferably bolted, to the roll body. Mounted in the trunnion flange are actuators connected to the insulating devices. It is preferred that at least one insulating device is configured in each of the thermal treatment conduits, and even more preferred that an insulating device is configured in each thermal treatment conduit at each end of the roll body. However, it may be sufficient that an insulating device be configured only at an inlet end of each of the thermal treatment conduits or in only selected thermal treatment conduits, such as in every other thermal treatment conduit.
In accordance with the invention, each of the insulating devices is elongatable in the longitudinal direction of the thermal treatment conduits. Furthermore, each of the actuators is mounted shiftable in the trunnion flange and fixable relative to the direction of shifting. Each of the actuators is connected to a shiftable part of one of the insulating devices and entrains this part in its own shifting movement. The connection is preferably totally rigid and may be, for example, a weld. In principle, however, any connection for joint shifting will do.
The insulating devices themselves may be configured directly thermally insulating in that, as an insulating intermediate layer, they reduce any heat transfer between the thermal treatment fluid and the roll. However, they may also be configured so that, although permitting direct contact of the thermal treatment fluid with the conduit wall in the conduit portion to be insulated, they hinder the flow of the thermal treatment fluid, and, thus, likewise reduce the heat transfer between the thermal treatment fluid and the roll as compared to an unrestricted flow.
In preferred embodiments, the insulating devices are configured telescopic, including at least two elements being shiftably one relative to the other, preferably one of the elements being fixedly located in the corresponding thermal treatment conduit and forming a thermally insulating longitudinal portion of the insulating device, preferably a rim end portion, and the other element or elements may be shifted by means of the actuators, and, thus, is or are also termed shifting element or elements in the following. The insulating device being elongatable in itself may also be formed in that a longitudinal portion of the insulating device, preferably a rim end portion thereof, is formed directly by a portion of the thermal treatment conduit, into and out of which a shifting element is shiftable. Formed in the thermal treatment conduit is a low-flow insulating space, so-to-speak a dead space. Such an insulating space is preferably configured as a blind hole having no through-flow downstream of an inlet and/or an outlet. In both embodiments, the shifting element overlaps at least in one of its shifting positions, preferably in all shifting positions, a longitudinal portion of the insulating device formed by another element arranged in the thermal treatment conduit or by being correspondingly formed by flow engineering. In further preferred embodiments, each of the insulating devices may also be configured in one piece, more particularly as an insulating bellows of, for example, a thermally insulating material or of metal which is concertined in the longitudinal direction of the thermal treatment conduit. In such a one-piece configuration, preferably an end of the insulating device is fixedly located in the corresponding thermal treatment conduit, and another end forms a shifting element, which may be shifted by means of an actuator. The individual elements of each of the insulating devices act thermally insulating and/or flow-obstructing in all of the embodiments described above.
A thermally insulating longitudinal portion may be formed, as aforementioned, by an insulator insert, purely by flow engineering, or by a combination of both measures. When configured by means of an insulator insert, this insulator insert is made preferably of a thermally insulating material, such as, for example, Teflon or a ceramic material. The insulating longitudinal portion may also be formed, likewise preferably, by configuring an insulating space in the form of an insulating gap between the wall of the thermal treatment conduit and the insulator insert. Although the insulating gap is filled with thermal treatment fluid, it has no, or no unhindered, through-flow of the thermal treatment fluid. The insulating gap is thus cut off from the fresh inflow of hot or cold thermal treatment fluid. The advantage of this variant of the embodiment is that the insulator insert may be produced particularly cost-effective, for example made of steel. In a preferred variant, such an insulating gap is formed by means of an insert sleeve comprising at its outer shell a recess, this recess forming the insulating gap between the sleeve and inner wall of the thermal treatment conduit.
A shifting element may be made of a thermally insulating material, for example Teflon or a ceramic material, to line the thermal treatment conduit in shielding the wall of the thermal treatment conduit from the thermal treatment fluid. In a preferred variant, it is shaped such that it forms an insulating space with the wall of the thermal treatment conduit which, although it may be filled with thermal treatment fluid, has no, or no free, throughflow of thermal treatment fluid. In this case, it may also be made of a thermally insulating material, advantageously however, it may also be made of any other material which satisfies the mechanical and thermal requirements. Instead of this, the shifting element may also be used to steer the flow of the fresh thermal treatment fluid so that an open insulating space materializes at the wall of the thermal treatment conduit without any, or without any appreciable, flow velocity. Also due to this, the heat transfer from the freely flowing thermal treatment fluid to the roll is strongly reduced.
An advantage of the elongatable actuator is that the shifting position of the shiftable insulator insert is explicitly defined by the position of the actuator. The actuator serves, at the same time, as an indicator for the set length of the insulating device. The position of the actuator can be ascertained very simply by means of a depth gauge, with which the distance between a face of the trunnion flange and a rear face of the actuator is measured.
In a preferred example embodiment, a means for positioning the actuator is formed by a spindle drive. For this purpose, a positioning spindle is rotary mounted non-shiftable in the trunnion flange, a screw thread of the positioning spindle and a screw thread of the actuator forming the spindle drive. By rotating the positioning spindle the linearly guided actuator can be moved back and forth. It is particularly preferred that a drive gearwheel is seated on the positioning spindle, this drive gearwheel being connected by means of a transmission member to positioning spindles of further actuators for a common positioning drive. Preferably, the shifting elements of all devices are shifted by means of actuators having such a common drive at at least one side of the roll.
Although elongating the insulating device and, in particular, varying the insulating length by telescoping a shifting element relative to a thermally insulating longitudinal portion, preferably fixedly located, of the insulating device is particularly of advantage in conjunction with the pure shifting coupling between the actuator and the shifting element, it also already offers decisive advantages by itself. For instance, no space needs to be configured in the trunnion flange, into which a part of the insulating device is traveled. The Applicant reserves the right to direct a separate set of claims to elongation of the insulating device, also without the shifting coupling in accordance with the invention, although the combination affords specific advantages.